[gdal-dev] Duplicate pixels in VRT

[Jon Morris]

Hello all,

I've come across a weird edge case and I'm wondering if anyone has seen something similar.

I'm updating our application from GDAL v2.2 to v3.2 and have a failing test where there is a 1 pixel shift in the output. We're building a VRT from a DTM and a flood depth raster and when you call ds.ReadAsArray() on the VRT there is a duplicated column of pixels at GDAL 2, which is causing the apparent shift. It's not worth raising a ticket, as the GDAL 3 output is correct, but I can't explain why this shift has happened and I'm wondering if this has happened anywhere else.

If I open the two VRTs in QGIS, they look the same, so maybe it's an issue with ReadAsArray. There is slight difference in SRS precision, which might be causing a rounding error, but otherwise I've no idea what might be causing it.

GDAL 2
<SRS>
PROJCS["North_America_Albers_Equal_Area_Conic",
GEOGCS["NAD83",DATUM["North_American_Datum_1983",
SPHEROID["GRS 1980",6378137,298.2572221010042,AUTHORITY["EPSG","7019"]],AUTHORITY["EPSG","6269"]],
PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433],AUTHORITY["EPSG","4269"]],
PROJECTION["Albers_Conic_Equal_Area"],
PARAMETER["standard_parallel_1",20],
PARAMETER["standard_parallel_2",60],
PARAMETER["latitude_of_center",40],
PARAMETER["longitude_of_center",-96],
PARAMETER["false_easting",0],
PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]]]
</SRS>

GDAL 3
<SRS dataAxisToSRSAxisMapping="1,2">
PROJCS["North_America_Albers_Equal_Area_Conic",
GEOGCS["NAD83",DATUM["North_American_Datum_1983",
SPHEROID["GRS 1980",6378137,298.257222101004,AUTHORITY["EPSG","7019"]],AUTHORITY["EPSG","6269"]],
PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4269"]],
PROJECTION["Albers_Conic_Equal_Area"],
PARAMETER["latitude_of_center",40],
PARAMETER["longitude_of_center",-96],
PARAMETER["standard_parallel_1",20],
PARAMETER["standard_parallel_2",60],
PARAMETER["false_easting",0],
PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Easting",EAST],AXIS["Northing",NORTH]]
</SRS>

Thanks,

Jon


Jon Morris
Software Developer

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